Class: Abachrome::Converters::OklchToLrgb

Inherits:
Base
  • Object
show all
Defined in:
lib/abachrome/converters/oklch_to_lrgb.rb

Instance Attribute Summary

Attributes inherited from Base

#from_space, #to_space

Class Method Summary collapse

Methods inherited from Base

#can_convert?, #convert, find_converter, #initialize, raise_unless, register

Constructor Details

This class inherits a constructor from Abachrome::Converters::Base

Class Method Details

.convert(oklch_color) ⇒ Object 



24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
 
# File 'lib/abachrome/converters/oklch_to_lrgb.rb', line 24

def self.convert(oklch_color)
  raise_unless oklch_color, :oklch

  l_oklch, c_oklch, h_oklch = oklch_color.coordinates.map { |_| AbcDecimal(_) }
  alpha = oklch_color.alpha

  # Step 1: OKLCH to OKLAB
  # l_oklab is the same as l_oklch
  l_oklab = l_oklch

  # Convert hue from degrees to radians
  # h_oklch is AbcDecimal, Math::PI is Float. AD(Math::PI) makes it AbcDecimal.
  # Division by AD("180") ensures AbcDecimal arithmetic.
  h_rad = (h_oklch * AD(Math::PI)) / AD("180")

  # Calculate a_oklab and b_oklab
  # Math.cos/sin take a float; .value of AbcDecimal is BigDecimal.
  # AD(Math.cos/sin(big_decimal_value)) wraps the result back to AbcDecimal.
  a_oklab = c_oklch * AD(Math.cos(h_rad.value))
  b_oklab = c_oklch * AD(Math.sin(h_rad.value))

  # Step 2: OKLAB to L'M'S' (cone responses, non-linear)
  # Constants from the inverse of M2 matrix (OKLAB to L'M'S')
  # l_oklab, a_oklab, b_oklab are already AbcDecimal.
  l_prime = l_oklab + (AD("0.39633779217376785678") * a_oklab) + (AD("0.21580375806075880339") * b_oklab)
  m_prime = l_oklab - (AD("0.1055613423236563494") * a_oklab) - (AD("0.063854174771705903402") * b_oklab)
  s_prime = l_oklab - (AD("0.089484182094965759684") * a_oklab) - (AD("1.2914855378640917399") * b_oklab)

  # Step 3: L'M'S' to LMS (cubing to linearize cone responses)
  l_lms = l_prime**3
  m_lms = m_prime**3
  s_lms = s_prime**3

  # Step 4: LMS to LRGB
  # Using matrix M_lrgb_from_lms (OKLAB specific)
  r_lrgb = (l_lms * AD("4.07674166134799")) + (m_lms * AD("-3.307711590408193")) + (s_lms * AD("0.230969928729428"))
  g_lrgb = (l_lms * AD("-1.2684380040921763")) + (m_lms * AD("2.6097574006633715")) + (s_lms * AD("-0.3413193963102197"))
  b_lrgb = (l_lms * AD("-0.004196086541837188")) + (m_lms * AD("-0.7034186144594493")) + (s_lms * AD("1.7076147009309444"))

  # Clamp LRGB values to be non-negative.
  # LRGB values can be outside [0,1] but should be >= 0.
  # Further clamping to [0,1] typically occurs when converting to display-referred spaces like sRGB.
  zero_ad = AD("0")
  output_coords = [
    [r_lrgb, zero_ad].max,
    [g_lrgb, zero_ad].max,
    [b_lrgb, zero_ad].max
  ]

  Color.new(ColorSpace.find(:lrgb), output_coords, alpha)
end